Crane control systems are known for cranes having crane actuators that can be hydraulically actuated by a so-called load sensing system. This allows different crane operations to be carried out independent of one another. The controller determines the pressure that is required by each crane actuator and calculates the maximum required pressure. The controller thereupon automatically sets the hydraulic pump to the calculated pressure.
This relates to safe and robust operation. The respective crane actuators can then be supplied with the hydraulic medium through proportional valves.
In the load-sensing system according to the prior art (also see FIG. 2), most loads are connected together hydraulically in the open hydraulic circuit. Only the rotating mechanism is separated, since it must also be operated in the “closed hydraulic circuit” mode.
However, each crane actuator requires an individual hydraulic pressure and an individual hydraulic flow rate.
The luffing cylinder typically requires a high hydraulic pressure, and a winch frequently requires a high hydraulic oil flow rate.
If the luffing mechanism requires 330 bar and 100 l/min and the winch, for example, a pressure of 60 bar and a hydraulic oil flow rate of 200 l/min, then the hydraulic pressure must be reduced in the proportional valve assigned to the winch. The difference between 300 bar−60 bar=240 bar is then reduced in the proportional valve and converted into heat. The power that is converted into heat in this case is approx. 80 kW. The following formula can be used in practice:
      P    ⁡          [      kW      ]        =                    PressureDifference        ⁡                  [          bar          ]                    *              VolumeFlowRate        ⁢                                  [                  l          ⁢                      /                    ⁢          min                ]              600  
It is clear that the “losses” become larger the greater the pressure difference and the greater the volumetric flow rate.
Thus the object of the present invention is to improve upon a crane control system of the type indicated here in an advantageous manner.
This objective is achieved according to the invention by a crane control system for controlling and/or for the hydraulic supply of hydraulic loads of a crane, having at least one first pump means and at least a second pump means, at least one first split control block and at least one second split control block is provided by means of which at least one hydraulic load of the crane can be respectively supplied with hydraulic medium, wherein the first pump means is connected to the first split control block and can be driven at a first hydraulic pressure, and wherein the second pump means is connected to the second split control block and can be driven at a second hydraulic pressure.
This gives rise to the advantage, in particular, that the first hydraulic load of a crane that must be supplied with the hydraulic medium at a low or relatively low operating pressure can be supplied without a corresponding reduction in the operating pressure of the hydraulic medium, for example, by the first pump means and the first split control block. In addition, a second hydraulic load, which must be supplied with hydraulic medium at a high or relatively high operating pressure, can be supplied directly at the appropriate operating pressure of the hydraulic medium, for example, by the second pump means and the second split control block.
It can be provided that at least one valve means is arranged or provided between the first split control block and the second split control block, by means of which the first split control block and the second split control block can be hydraulically connected and/or separated. A hydraulic short circuit can advantageously be produced by opening it, so that, for example, more rapid crane operations are possible if needed. In this case the previously mentioned power losses must be accepted as a consequence of the necessary pressure reduction.
It is also possible that at least one switching means is provided by which the valve means can be actuated. The crane operator can be cognizant of the energy saving crane control system that has changeover control blocks that are separated from one another by the valve means, i.e., not switching hydraulically short circuited changeover control blocks, through the switching means, which can be a switch or a so-called “economy switch”. Splitting into the at least two changeover control blocks can thereby be activated by the crane operator when the instantaneous situation enables energy to be saved. The crane operator activates the “economy switch” directly in this case in order to turn on the energy saving function. If the crane operator knows in advance that he often requires high volumetric flow rates of the hydraulic medium for continuous lifting operations with the crane, based on the necessary actuation of hydraulic loads of the crane at high operating pressures of the hydraulic medium, the economy switch is not activated, or is suitably switched or deactivated.
In addition, it can also be provided that at least one third pump means and at least one third split control block is provided, by which at least one hydraulic load of the crane can be supplied with hydraulic medium, wherein the third pump means is connected to the third split control block and can be driven by a third hydraulic pressure.
It is furthermore possible that at least one second valve means is arranged or provided between the third split control block and the first split control block and/or the second split control block, by which the third split control block can be hydraulically connected and/or disconnected from the first split control block and/or the second split control block.
It is also possible that at least one additional switching means is provided by means of which the second valve means can be actuated and/or that it is also possible to actuate the second valve means through the switching means by which the valve means can be actuated.
It can be provided that at least one crane control element, in particular a crane controller, is provided by which the at least one first hydraulic pressure and/or the at least one second hydraulic pressure is adjustable, wherein it is further advantageously provided that the third hydraulic pressure can be adjusted by the crane control system.
In addition, it is possible that the first or second hydraulic pressures can be equalized by the crane control element, wherein the respective lower hydraulic pressure can advantageously be equalized to the higher hydraulic pressure and thereby increased.
Furthermore, it can be provided that the respective at least one hydraulic load of the crane is a crane actuator, wherein the crane actuator is in particular a rotating mechanism, a luffing cylinder, a winch, a telescoping drive mechanism and/or a caterpillar drive.
Hydraulic loads, and thus crane actuators, can in particular be luffing cylinders, telescoping cylinders, caterpillar drives, auxiliary loads (e.g., luffing or telescoping of the cabin arms, ballast cylinders) and/or winches for lifting operations or luffing mechanisms.
In addition, the present invention relates to a crane having the features of claim 10. It is accordingly provided that the crane is provided with at least one crane control system according to one of the claims 1 to 9. The crane can, for example, be a mobile crane.
Additional details and advantages of the invention will now be explained with the aid of the embodiments shown in greater detail in the drawings.